00 CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



will demonstrate. This figure represents a fossil shell (Euomphalus ?) found by Mr. E. M. 

 Balfour of Trinity College, Cambridge, in the Carboniferous Limestone of Haddington- 

 shire, about three miles from Dunbar. On grinding the specimen it was found that what 

 had been the empty cavity of the shell was partially occupied by the remains of Saccamminae 

 which, when living, had taken up their abode there, and a chain of fusiform segments 

 was exposed exactly as it appears in the drawing. Making a little allowance for the 

 irregularity of the line of growth, it may be assumed that one segment has been out of 

 the plane of the section and has been ground off, and if so this individual specimen has 

 consisted of not less than eleven chambers united by stoloniferous tubes. 



The test of Saccammina is essentially composite and arenaceous, the constituent 

 particles being fitted and cemented together so as to give a nearly smooth exterior. The 

 interior surface varies a good deal in different specimens. Sometimes it is nearly smooth, 

 or roughened only by the projecting angles of the constituent sand-grains, which are 

 usually much smaller in size than those selected by the recent species for shell-building 

 purposes. In other cases the inner surface is covered with a network of short delicate 

 labyrinthic growths, as seen in PI. I, fig. 5. 



Peculiar conditions of infiltration render it very difficult to speak in positive 

 terms concerning the minute structure of the test. Plate I, fig. G, represents a highly 

 magnified tangential section which, though insufficient for the determination of the size 

 or form of the constituent sand-grains, demonstrates clearly enough the arenaceous 

 structure of the test both in its compact and labyrinthic portions. 



There may frequently be observed on the exterior of the segments minute circular 

 scars, of which Plate I, fig. 7, is an example. They are formed of three, four, or more 

 slightly raised, granular, concentric rings, the outermost having a diameter of a thirtieth 

 of an inch (0'85 mm.) or less. It is not easy to offer a satisfactory explanation in respect 

 to them, but they are of too frequent occurrence and too uniform in character not to 

 have a meaning, and therefore cannot be passed over entirely without notice in some 

 cases they look like the result of the repair of an injury to the test. 



In the Saccammina limestone, the matrix is usually softer than the fossils embedded 

 in it, and frequently the infiltrated matter which occupies the interior of the segments is 

 harder than the fossilized test. Chemical analysis being resorted to for an explanation, it 

 was found that some specimens of the rock contained a very large percentage of 

 silica. If a number of segments of Saccammina from the disintegrated rock be broken, 

 it will be found that the interior of each is occupied either by a smooth amorphous cast 

 completely filling the cavity, or, much less frequently, by a loose tuft of crystals. The 

 amorphous casts have been found to consist of colloid silica ; the crystalline tufts (Plate I, 

 fig. 5), of carbonate of lime. The mineral contents of a large number of chambers, 

 taken at random from a piece of the weathered Elfhills Limestone, yielded more than 

 90 per cent, by weight of silica, whilst the tests themselves were almost purely 

 calcareous. 



